1. Field of the Invention
The present invention relates to a steering system for a vehicle, including a driving pulley connected to a steering wheel and a follower pulley connected to a gear box for steering vehicle wheels. The driving and follower pulleys are interconnected by a wire, so that a steering torque inputted to the steering wheel is transmitted to the gear box through the wire.
2. Description of the Prior Art
A conventional steering system for a vehicle includes a steering shaft which has a steering wheel at its upper end and which is connected to a gear box at its lower end. Steering torque inputted to the steering wheel, is transmitted through the steering shaft to a rack and pinion mechanism provided within the gear box.
However, the conventional steering system has a problem because the steering wheel and the gear box are interconnected by the steering shaft, and it is difficult to freely select the position of the steering wheel relative to the gear box and hence, not only is freedom of design considerably limited, but also the gear box cannot be commonly used for a right-side steering wheel vehicle and a left-side steering wheel vehicle. Moreover, the conventional steering system has another problem in that vibration from a road surface to tires and vibration of the engine are applied to the steering wheel through the steering shaft. For this reason, silence within a vehicle compartment and the riding comfort are disturbed by the vibrations.
Therefore, it may be proposed that a flexible transmitting means such as a Bowden wire is used in place of the conventional steering shaft. In such a case, it is possible to freely select the position of the steering wheel relative to the gear box. Moreover, the vibration of the gear box is transmitted to the steering wheel and is substantially reduced hence, the above-described problems can be overcome.
When the flexible transmitting means such as the Bowden wire is used in place of the conventional steering shaft, however, the friction provided by the sliding movement between the outer tube and the inner cable of the wire is significantly larger as compared with the friction of the conventional steering shaft. Therefore, the steering torque of the steering wheel is transmitted to the gear box through the wire which produces large friction. If a steering torque detecting means is provided within the gear box, it is difficult to accurately detect the steering torque due to the friction.
More specifically, when the steering torque inputted to the steering wheel increases, the steering torque is not wholly transmitted to the gear box due to the friction and as a result, there is a possibility that the steering torque is detected as a value smaller than an actual value. When the steering torque inputted to the steering wheel decreases, a portion of the steering torque provided theretofore remains in the gear box due to the friction and as a result, there is a possibility that the steering torque is detected as a value larger than an actual value. If the steering torque cannot be correctly detected for such a reason, it is difficult to appropriately control a power-steering motor, resulting in a reduced steerage feeling.